The primary objectives of this protocol are to determine the influence of virus load and CD4 counts, biologic phenotype and the presence of symptoms of HIV disease on responses to new therapeutic regimens in HIV- infected individuals who have received either ZDV or ddI monotherapy. Antiretroviral drug resisitance will also be determined looking for the devel opment of the 184 pol gene mutation in response to ZDV and 3TC and the development of ZDV resistance mutations. Antiretroviral effects will be evaluated by short and long term suppression of HIV plasma RNA.